Superluminal communication

Superluminal communication is the term used to describe the hypothetical process by which one might send information at faster-than-light (FTL) speeds. Scientific investigation has thus far produced no empirical evidence for superluminal communication.

Some theories and experiments include:

Group velocity > c experiments
evanescent wave coupling
Tachyons
Quantum non-locality

According to the currently accepted theory, three out of those four phenomena do not produce superluminal communication — although they may give that appearance under some conditions. Only tachyons (which are generally thought to be theoretically impossible) produce truly superluminal communication.